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Objectives The main objective of this study was to evaluate the diagnostic accuracy of two novel biomarkers, calprotectin (CP) and serum amyloid A (SAA), along with the more traditional inflammatory markers C-reactive protein (CRP) and white blood cell count (WBC), in patients suspected of having acute appendicitis (AA). The secondary objective was to compare diagnostic accuracy of these biomarkers with a clinical scoring system and radiologic imaging. Methods A total of 233 patients with suspected AA, presenting to the emergency department (ED) between January 2010 and September 2010, and 52 healthy individuals serving as controls, were included in the study. Blood was drawn and CP and SAA−1 concentrations were measured using enzyme-linked immunosorbent assay (ELISA). CRP and WBC concentrations were routinely measured and retrospectively abstracted from the electronic health record, together with physical examination findings and radiologic reports. The Alvarado score was calculated as a clinical scoring system for AA. Final diagnosis of AA was based on histopathologic examination. The Mann-Whitney U-test was used for between-group comparisons. Receiver operating characteristic (ROC) curves were used to measure the diagnostic accuracy for the tests and to determine the best cutoff points. Results Seventy-seven of 233 patients (33%) had proven AA. Median plasma levels for CP and SAA−1 were significantly higher in patients with AA than in those with another final diagnosis (CP, 320.9 ng/mL vs. 212.9 ng/mL; SAA−1, 30 mg/mL vs. 0.6 mg/mL; p 7). Ultrasound (US) had a sensitivity of 84% and a specificity of 94%. Computed tomography (CT) had a sensitivity of 100% and a specificity of 91%. The area under the ROC (95% confidence interval [CI]) was 0.67 (95% CI = 0.60 to 0.74) for CP, 0.76 (95% CI = 0.70 to 0.82) for SAA, 0.71 (95% CI = 0.64 to 0.78) for CRP, and 0.79 (95% CI = 0.73 to 0.85) for WBC. No cutoff points had high enough sensitivity and specificity to accurately diagnose AA. However, a high sensitivity of 97% was shown at 7.5 × 109/L for WBC and 0.375 mg/mL for SAA. Conclusions CP, SAA−1, CRP, and WBC were significantly elevated in patients with AA. None had cutoff points that could accurately discriminate between AA and other pathology in patients with suspected AA. A WBC < 7.5 × 109/L, with a low level of clinical suspicion for AA, can identify a subgroup of patients who may be sent home without further evaluation, but who should have available next-day follow-up. Resumen Evaluacion de la Certeza Diagnostica de Marcadores Plasmaticos para el Diagnostico Precoz en los Pacientes con Sospecha de Apendicitis Aguda Objetivos El principal objetivo de este estudio fue evaluar la certeza diagnostica en los pacientes con sospecha de tener una apendicitis aguda de dos nuevos biomarcadores, la calprotectina (CP) y el amiloide A serico (AAS), junto con los marcadores inflamatorios mas tradicionales, como la proteina C reactiva (PCR) y el numero de leucocitos. El objetivo secundario fue comparar la certeza diagnostica de estos biomarcadores con un sistema de puntuacion clinica y la imagen radiologica. Metodologia Se incluyeron en este estudio 233 pacientes con sospecha de apendicitis que acudieron al servicio de urgencias (SU) entre enero de 2010 y septiembre de 2010, y 52 individuos sanos que sirvieron como controles. Se extrajo sangre y se midio la CP y el AAS mediante un ELISA. La PCR y el numero de leucocitos se midieron de forma rutinaria y se recogieron de forma retrospectiva de las historias clinicas electronicas, junto con los hallazgos de la exploracion fisica y los informes radiologicos. La escala Alvarado (Alvarado score) se calculo como un sistema de puntuacion clinica para la apendicitis aguda. El diagnostico final de apendicitis aguda se baso en el examen histopatologico. Se utilizo el test de la U de Mann-Whitney para la comparacion entre los grupos. Las curvas ROC se utilizaron para medir la certeza diagnostica de las pruebas diagnosticas y para determinar los mejores puntos de corte. Resultados Setenta y siete de 233 pacientes (33%) tuvieron apendicitis aguda con certeza. Las medianas de los niveles plasmaticos de CP y AAS fueron significativamente mas altas en los pacientes con apendicitis aguda que en aquellos con otro diagnostico final (CP 321 ng/mL vs. 213 ng/mL; AAS 30 mg/mL vs. 0,6 mg/mL; p 7). La ecografia tuvo una sensibilidad de un 84% y una especificidad de un 94%. La tomografia computarizada (TC) tuvo una sensibilidad de un 100% y una especificidad de un 91%. La curva ROC (intervalo de confianza 95%) fue de 0,67 (IC 95% = 0,60 a 0,74) para la CP, de 0,76 (IC 95% = 0,70 a 0,82) para la AAS, de 0,71 (IC 95%= 0,64 a 0,78) para la PCR y de 0,79 (IC 95%= 0,73 a 0,85) para los leucocitos. Conclusiones La CP, la AAS, la PCR y el numero de leucocitos estaban significativamente elevados en los pacientes con apendicitis aguda. No hay un punto de corte que pueda discriminar de forma certera entre la apendicitis aguda y otra patologia en los pacientes con sospecha de apendicitis aguda. Un numero de leucocitos